1. Field of the Invention
The present invention relates to an electronic controller for a surgical laser system and more particularly to an electronic controller which not only controls the pulse width of a beam of light energy from a surgical laser system a within a range of 0.005 seconds to 0.100 seconds, but also limits the maximum number of pulses to a number which a surgeon may select for use in surgical procedures.
2. Description of the Prior Art
U.S. Pat. No. 3,982,541, entitled Eye Surgical Instrument, issued to Francis A. L'Esperance on Sept. 28, 1976, teaches a method of surgically removing body tissue which includes the steps of contacting the body tissue with a probe open at a free end, passing a CO.sub.2 laser beam through a central passage in the probe and the open end to the tissue at a power level sufficient to affect vaporization of tissue, vaporizing only the surface portion of the tissue exposed to the CO.sub.2 laser beam in a manner so that the vaporizing step is surface phenomena at a depth not more than about 0.33 millimeters, introducing a gas stream into the probe downstream from the lenses associated with the CO.sub.2 laser beam, passing the gas stream through the probe in a direction towards the free end of the probe and out of the probe, and removing smoke and any vaporized portion of the tissue through the probe by way of the gas stream.
U.S. Pat. No. 4,122,853, entitled Infrared Laser Photocautery Device, issued to Michael R. Smith on Oct. 31, 1978, teaches an apparatus and a method for cauterizing biological tissue while providing isolation from surrounding absorbing tissue and fluid media. The device includes a probe having a special window through which an infrared laser beam is directed to cauterize the biological tissue. The device also includes an infrared laser beam generator, a control circuit for controlling the intensity and duration of the laser beam and an articulating arm for directing the laser beam to the probe. The probe includes a hollow, laser light guide tube which has an infrared transparent window in its tip which permits the tip to be brought into contact with biological tissue to be cauterized while excluding the surrounding absorbing tissue from the effects of the beam.
In their article, entitled "The Use of the Laser in Neurological Surgery," published in Surgical Neurology, Volume 14, Number 1, pages 1-10, July, 1981, Myles L. Saunders, Harold F. Young, Donald P. Becker, Richard P. Greenberg, Pauline G. Newlon, Richard L. Corales, William T. Ham, and John T. Povlishock discuss the use of a CO.sub.2 laser system in neurological surgery.
U.S. Pat. No. 3,710,798, entitled Laser System for Microsurgery, issued to Herbert C. Bredemeier on Jan. 16, 1973, teaches a laser system for microsurgery which includes a mirror for changing the direction of a beam of light energy from a CO.sub.2 laser system and directing the beam to the treatment site.
U.S. Pat. No. 4,169,251, teaches Waveguide Gas Laser with High Freqency Transverse Discharge Excitation, issued to Katherine D. Laakman on Sept. 25, 1979, teaches a waveguide laser which is excited by means of a transverse discharge at radio frequencies generally in the vhf-uhf range, i.e., from about 30 MHz to about 3 GHz. These excitation frequencies are sufficiently high to ensure negligible interaction of discharge electrons with the discharge-establishing electrodes, thereby achieving superior discharge properties which result in a laser of improved performance and reduced size and complexity.
In their article, entitled "A Flexible Sealed Tube Transverse Radio Frequency Excited Carbon Dioxide Laser for Dermatologic Surgery," published in Lasers in Surgery and Medicine, Volume 2, Number 4, pages 317-332, 1983, Leon Goldman, Edward Perry, David Stefanovsky discuss a CO.sub.2 laser system which has been found effective for dermatological surgery. The CO.sub.2 laser system is a radio frequency transversely excited waveguide CO.sub.2 laser systems.
In their article, entitled "Arterial response to laser operation for removal of atherosclerotic plaques," published in The Journal of Thoracic and Cardiovascular Surgery, Volume 85, Number 3, pages 409-421, March, 1983, Ross G. Gerrity, Floyd D. Loop, Leonard A. R. Golding, L. Allen Erhart, and Zsolt B. Argenyi, report that they have performed a series of experiments on using a beam of light energy from a CO.sub.2 surgical laser system, which is Coherent's System 400, to vaporize plaque in coronary arteries of swines. They have used a beam of light energy having a diameter of 0.9 millimeters. They have varied the power of the beam of light energy from 10.0 watts to 40.0 watts for exposed time periods between 0.1 second and 1.0 second. They have used amounts of energy ranging from 1.0 joule to 40.0 joules. When they have used 1.0 joule of energy, they have vaporized 0.15 cubic millimeters of plaque material.
In order to understand the theory of operation of the controller it is necessary to understand the following set of theoretical and experimental calculations for the use of the CO.sub.2 laser system in surgery. The following definitions are used: d, which is the spot size, is the diameter of a beam of light energy; A is the area of the beam of light energy; P is the power of the beam of light energy; t is the total duration of the beam of light energy; .DELTA.t is the pulse width of an increment of the beam of the light energy; .DELTA.l is the cutting depth of an increment of beam of light energy; .DELTA.V is the volume of tissue vaporized by the increment of the beam of light energy and equals area of the beam of light energy multiplied by cutting depth of an increment of the beam of light enegy, A.DELTA.l.
The intensity, I, of the beam of light energy equals power divided by area, P/A. The amount of energy, E, delivered by the beam of light energy equals power multiplied by the total duration, Pt. The amount of energy, .DELTA.E, delivered by an increment of the beam of light energy equals power multiplied by its pulse width, P.DELTA.t. The energy density, R, is the amount of energy which is delivered by the increment of the beam of light energy divided by the volume of tissue in vaporized by the increment of the beam of light energy, .DELTA.E/.DELTA.V.
In their article, entitled "Laser Energy in Arthoscopic Meniscectomy," published in Orthopedics, Volume 6, Number 9, pages 1165-1169, September, 1983, Terry L. Whipple, Richard B. Caspari and John F. Meyers discuss the rationale and technique for performing arthoscopic meniscectomy with a carbon dioxide laser. They present findings of limited rabbit and human studies. They have used a CO.sub.2 laser system, which is similar to the one which Gerrity et al, supra, have used and which provides a two millimeter spot size at a power setting varying between ten and ninety watts, to vaporize a portion of the meniscus. They have used the CO.sub.2 laser system at a power setting of thirty watts having a pulse duration of 0.2 seconds to provide six joules of light energy in order to produce a crater which is two millimeters in diameter and which is 1.5 millimeters in depth. The volume of tissue which they have vaporized is 4.71 cubic millimeters.
In chapter 15, entitled "Basic principles arthoscopic surgery," of his book, entitled Diagnostic and Surgical Arthoscopy: The Knee and Other Joints, published by The C. V. Mosby Company, 1981, Lanny L. Johnson discusses the principles of arthoscopic surgery including proper techniques, proper portals of entry, the types of arthoscope to be utilized in the triangulation technique. He stresses that arthoscopic surgery decreases the morbidity over standard arthrotomy procedure.
In chapter 16, entitled, "Meniscal surgery," of his book, Johnson delineates the type of meniscal surgery. He bases the type of arthoscopic surgery necessary on the location of the tear, the extent of the tear and the nature of the adjacent joint. He stresses excising a minimal amount of the meniscus so that the remaining essentially normal meniscus can function biomechanically as a "washer" and "stabilizer" between the tibia and femur.
U.S. Pat. No. 4,369,768, entitled Arthoscope, issued to Marko Vukovic on Jan. 25, 1983, teaches an arthoscope.
U.S. Pat. No. 4,289,132, entitled Surgical Instrument and Method of Using the Same, issued to Robert D. Rieman on Sept. 15, 1981, teaches a surgical instrument which has a slender rod with a sharp point which is pushed inside out through skin tissue at a location remote from an incision so that the rod can be manipulated to perform a surgical procedure at the remote location by means of a surgical tool mounted on the other end of the rod.
U.S. Pat. Nos. 3,221,744, 3,835,859 and 4,067,340 teach surgical instruments for performing the posterior detachment of the meniscus which are relatively difficult to use and sometime fail to provide the desired detachment of the posterior part of the meniscus. The stopping of active bleeding, or hemostasis, is very difficult to achieve in a meniscectomy because of the inaccessibility of the posterior portion of the knee joint. Thus a meniscectomy is almost always performed with a tourniquet on the upper thigh and the tourniquet is not released until the surgical operation has been completed and a dressing and a compressive bandage applied to the knee joint which usually fills with blood. This post-operative bleeding contributes to the patient's pain and discomfort and the slowing of post-operative recovery.
In their article, entitled "Long-term clinical assessment of the efficacy of adjunctive coronary endarterectomy," published in The Journal of Thoracic and Cardiovascular Surgery, Volume 81, Number 1, pages 21-29, January 1981, D. Craig Miller, Edward B. Stinson, Philip E. Oyer, Bruce A. Reitz, Stuart W. Jamieson, Ricardo J. MorenoCabral and Norman E. Shumway demonstrate in a retrospective review the efficacy of right coronary endarterectomy. In their study they have found that the long-term survival following endarterectomy to be not statistically different from patients undergoing coronary bypass surgery alone. Despite a two-fold increase in the perioperative infarction rate with coronary endarterectomy, they have observed no differences in early mortality.
In their paper, entitled "Laser Endarterectomy in Vivo," Paper Number 1465 of Abstracts, published in Circulation, Supplement II, page II-366, October, 1982, Michael R. Treat, Francis M. Weld, John White, Kenneth A. Forde, John Fenoglio, Francis A. L'Esperance and Arthur B. Voorhees report they have studied the degree of injury and rate of healing of the arterial intima in New Zealand white rabbits. They have used a CO.sub.2 laser system to produce a beam of light energy having a power intensity of 2.0 to 20.0 watts per square millimeters for a duration of 0.100 second to create an intimal crater. They have demonstrated that vascular injury has consisted of (1) an impact crater and (2) an adjacent zone of necrosis and that, if the zone of necrosis is sufficiently large, then thrombosis will occur within 24 hours. They have also demonstrated that intitmal healing is remarkably complete if thrombosis is avoided.
In their article, entitled "Effects of Carbon Dioxide, Nd-YAG, and Argon Laser Radiation on Coronary Atheromatous Plaques," published in the Section on Coronary Heart Disease, The American Journal of Cardiology, Volume 50, Number 6, pages 1199-1205, December, 1982, George S. Abela, Sigurd Normann, Donald Cohen, Robert L. Feldman, Edward A. Geiser and C. Richard Conti have reported their study of the comparative effects of light energy from different types of laser systems. They have demonstrated that the degree of arterial injury correlates with the total energy delivered. Total energy in joules is calculated by the product of the amount of power in watts and the duration of the exposure time in seconds. They have used a CO.sub.2 laser system, a Nd:YAG laser system, and an Argon laser system. Irrespective of the wavelength of light energy there are three zones of arterial injury which occur. Tissue vaporization causes the first zone which is an impact crater. The second zone is a region of thermally induced necrosis and coagulation exist between 5 to 15 microns. The third zone is a region of acoustic and shock injury up to 30 microns.
U.S Pat. No. 3,730,185, entitled Endarterectomy Apparatus, issued to William Cook and Everett R. Lerwick on May 1, 1973, teaches an apparatus for removing arteriosclerotic material from an artery.
U.S Pat. No. 3,730,185, entitled Endarterectomy Apparatus, issued to Albert K. Chin on Sept. 22, 1981, teaches a center pull cutting annulus which is radially expansible to achieve complete removal of arteriosclerotic material from occluded arteries.
U.S. Pat. No. 3,929,238, entitled Sub-Intimal Dissection and Methods for Performing Endarterectomies Therewith, issued to Eli Curt on Dec. 30, 1975, teaches a sub-intimal dissector for removing arteriosclerotic material from an occluded artery.
U.S. Pat. No. 4,207,874, entitled Laser Tunnelling Device, issued to Daniel S. J. Choy on June 17, 1980, teaches to pass light energy from an Argon laser system into the artery of interest. The Argon laser system has been used with a power output is 4.5 watts and an exposure time of 36 seconds and has been found to be effective in restoring a 1.0 centimeter lumen in a completely thrombosed femoral artery.
U.S. Pat. No. 3,865,113, entitled Laser Device Particularly Useful as Surgical Scalpel, issued to Uzi Sharon and Isaac Kaplan on Feb. 11, 1975, teaches a laser beam manipulator including a tube which is optically coupled through an articulated arm to a CO.sub.2 laser system and a beam targeting member which is carried by the tube.
U.S. Pat. No. 4,226,548, entitled Apparatus For and Method of Utilizing Energy to Excise Pathological Tissue, issued to S. K. Davi on May 12, 1982, teaches a collimator which is optically coupled through an articulated arm to a CO laser system and which reduces the cross-section of a beam of light energy from the CO.sub.2 laser system.
In their article, entitled "Arterial response to laser operation for removal of atherosclerotic plaques," Gerrity et al have provided the following experimental values: P equals 10.0 watts; .DELTA.t equals 0.1 second; .DELTA.E equals 1.0 joule; the depth of the burn crater, .DELTA.1.sub.b, equals 0.1 millimeter; the area of tbe burn crater, A.sub.b, equals 1.5 square millimeters; the volume of the burn crater vaporized by 1.0 joule of energy, .DELTA.V.sub.b, equals 0.15 cubic millimeters. The energy density wbich is defined by the equation, R=.DELTA.E/.DELTA.V.sub.b, equals 6.67 joules per cubic millimeters. The beam diameter, d, equals 0.9 millimeters; the beam area, A, equals 0.636 millimeters so that the beam intensity which is defined the equation I=P/A, equals 15.72 watts per square millimeters.